document.write( "Question 924656: A man rows a boat 630 feet upstream against a constant current in 18 minutes. He then rows 405 feet downstream (with the same current) in 9 minutes. Find the speed of the current and the equivalent rate at which he can row in still water. \n" ); document.write( "
Algebra.Com's Answer #561026 by ankor@dixie-net.com(22740)\"\" \"About 
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A man rows a boat 630 feet upstream against a constant current in 18 minutes.
\n" ); document.write( " He then rows 405 feet downstream (with the same current) in 9 minutes.
\n" ); document.write( " Find the speed of the current and the equivalent rate at which he can row in still water.
\n" ); document.write( ":
\n" ); document.write( "let s = his rowing speed in still water in ft/min
\n" ); document.write( "let c = the speed of the current
\n" ); document.write( "then
\n" ); document.write( "(s-c) = effective speed upstream
\n" ); document.write( "and
\n" ); document.write( "(s+c) = effective speed downstream
\n" ); document.write( "write a distance equation for each way.(dist = time*speed)
\n" ); document.write( "18(s-c) = 630
\n" ); document.write( " 9(s+c) = 405
\n" ); document.write( "simplify both equations, divide the 1st by 18 and the 2nd by 9
\n" ); document.write( "we can use elimination very easily here
\n" ); document.write( "s - c = 35
\n" ); document.write( "s + c = 45
\n" ); document.write( "-------------Adding eliminates c, find s
\n" ); document.write( "2s = 80
\n" ); document.write( "s = 40 ft/min in still water
\n" ); document.write( ":
\n" ); document.write( ":
\n" ); document.write( "Check this, find the speed of the current
\n" ); document.write( "40 + c = 45
\n" ); document.write( "c = 5 ft/min
\n" ); document.write( "then the effective speed upstream will be 35 ft/min
\n" ); document.write( "18 * 35 = 630 ft
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